Download grade vii and viii - Sacred Heart CMI Public School

7th & 8th GRADE- SYLLABUS.
Our Solar System
Formation and evolution
The Solar System formed 4.568 billion years ago from the
gravitational collapse of a region within a large molecular
cloud. This initial cloud was likely several light-years across and
probably birthed several stars. As is typical of molecular clouds,
this one consisted mostly of hydrogen, with some helium, and
small amounts of heavier elements fused by previous generations
of stars. As the region that would become the Solar System,
known as the pre-solar nebula, collapsed, conservation of angular
momentum caused it to rotate faster. The centre, where most of
the mass collected, became increasingly hotter than the
surrounding disc. As the contracting nebula rotated faster, it
began to flatten into a proto planetary disc with a diameter of
roughly 200 AU and a hot, dense proto star at the centre. The
planets formed by accretion from this disc, in which dust and gas
gravitationally attracted each other, coalescing to form ever larger
bodies. Hundreds of proto planets may have existed in the early
Solar System, but they either merged or were destroyed, leaving
the planets, dwarf planets, and leftover minor bodies.
Due to their higher boiling points, only metals and silicates could
exist in solid form in the warm inner Solar System close to the
Sun, and these would eventually form the rocky planets of
Mercury, Venus, Earth, and Mars. Because metallic elements only
comprised a very small fraction of the solar nebula, the terrestrial
planets could not grow very large. The giant planets (Jupiter,
Saturn, Uranus, and Neptune) formed further out, beyond the
frost line, the point between the orbits of Mars and Jupiter where
material is cool enough for volatile icy compounds to remain
solid. The ices that formed these planets were more plentiful than
the metals and silicates that formed the terrestrial inner planets,
allowing them to grow massive enough to capture large
atmospheres of hydrogen and helium, the lightest and most
abundant elements. Leftover debris that never became planets
congregated in regions such as the asteroid belt, Kuiper belt,
and Oort cloud.
Within 50 million years, the pressure and density of hydrogen in
the centre of the proto star became great enough for it to
begin thermonuclear fusion. The temperature, reaction rate,
pressure, and density increased until hydrostatic equilibrium was
achieved: the thermal pressure equaled the force of gravity. At
this point, the Sun became a main-sequence star. The main-
sequence phase, from beginning to end, will last about 10 billion
years for the Sun compared to around two billion years for all
other phases of the Sun's pre-remnant life combined. Solar wind
from the Sun created the heliosphere and swept away the
remaining gas and dust from the proto planetary disc into
interstellar space, ending the planetary formation process. The
Sun is growing brighter; early in its main-sequence life its
brightness was 70% that of what it is today.
The Solar System will remain roughly as we know it today until
the hydrogen in the core of the Sun has been entirely converted to
helium, which will occur roughly 5 billion years from now. This
will mark the end of the Sun's main-sequence life. At this time,
the core of the Sun will collapse, and the energy output will be
much greater than at present. The outer layers of the Sun will
expand to roughly 260 times its current diameter, and the Sun
will become a red giant. Because of its vastly increased surface
area, the surface of the Sun will be considerably cooler (2,600 K at
its coolest) than it is on the main sequence. The expanding Sun is
expected to vaporize Mercury and Venus and render Earth
uninhabitable as the habitable zone moves out to the orbit of
Mars. Eventually, the core will be hot enough for helium fusion;
the Sun will burn helium for a fraction of the time it burned
hydrogen in the core. The Sun is not massive enough to
commence the fusion of heavier elements, and nuclear reactions
in the core will dwindle. Its outer layers will move away into
space, leaving a white dwarf, an extraordinarily dense object, half
the original mass of the Sun but only the size of Earth. The ejected
outer layers will form what is known as a planetary nebula,
returning some of the material that formed the Sun—but now
enriched with heavier elements like carbon—to the interstellar
medium.
THE SUN
The Sun is the Solar System's star and by far its most massive
component. Its large mass (332,900 Earth masses) produces
temperatures and densities in its core high enough to
sustain nuclear fusion of hydrogen into helium, making it a mainsequence star. This releases an enormous amount of energy,
mostly radiated into space as electromagnetic radiation peaking
in visible light.
The Sun is a G2-type main-sequence star. Hotter main-sequence
stars are more luminous. The Sun's temperature is intermediate
between that of the hottest stars and that of the coolest stars. Stars
brighter and hotter than the Sun are rare, whereas substantially
dimmer and cooler stars, known as red dwarfs, make up 85% of
the stars in the Milky Way.
The Sun is a population I star; it has a higher abundance of
elements heavier than hydrogen and helium ("metals" in
astronomical parlance) than the older population II
stars. Elements heavier than hydrogen and helium were formed
in the cores of ancient and exploding stars, so the first generation
of stars had to die before the Universe could be enriched with
these atoms. The oldest stars contain few metals, whereas stars
born later have more. This high metallicity is thought to have
been crucial to the Sun's development of a planetary
system because the planets form from the accretion of "metals
INNER PLANETS.
The four inner or terrestrial planets have
dense, rocky compositions, few or no moons, and no ring
systems. They are composed largely of refractory minerals, such
as the silicates, which form their crusts and mantles, and metals,
such as iron and nickel, which form their cores. Three of the four
inner planets (Venus, Earth and Mars)
have atmospheres substantial enough to generate weather; all
have impact craters and tectonic surface features, such as rift
valleys and volcanoes. The term inner planet should not be
confused with inferior planet, which designates those planets that
are closer to the Sun than Earth is (i.e. Mercury and Venus)
Mercury
Mercury (0.4 AU from the Sun) is the closest planet to the
Sun and the smallest planet in the Solar System (0.055 Earth
masses). Mercury has no natural satellites; besides impact
craters, it’s only known geological features are lobed ridges
or rupes that were probably produced by a period of
contraction early in its history. Mercury's very tenuous
atmosphere consists of atoms blasted off its surface by the
solar wind. Its relatively large iron core and thin mantle
have not yet been adequately explained. Hypotheses include
that its outer layers were stripped off by a giant impact; or,
that it was prevented from fully accreting by the young
Sun's energy.
Venus
Venus (0.7 AU from the Sun) is close in size to Earth (0.815
Earth masses) and, like Earth, has a thick silicate mantle
around an iron core, a substantial atmosphere, and evidence
of internal geological activity. It is much drier than Earth,
and its atmosphere is ninety times as dense. Venus has no
natural satellites. It is the hottest planet, with surface
temperatures over 400 °C (752°F), most likely due to the
amount of greenhouse gases in the atmosphere. No
definitive evidence of current geological activity has been
detected on Venus, but it has no magnetic field that would
prevent depletion of its substantial atmosphere, which
suggests that its atmosphere is being replenished by volcanic
eruptions.
Earth
Earth (1 AU from the Sun) is the largest and densest of the
inner planets, the only one known to have current geological
activity, and the only place where life is known to exist. Its
liquid hydrosphere is unique among the terrestrial planets,
and it is the only planet where plate tectonics has been
observed. Earth's atmosphere is radically different from
those of the other planets, having been altered by the
presence of life to contain 21% free oxygen. It has one
natural satellite, the Moon, the only large satellite of a
terrestrial planet in the Solar System.
Mars
Mars (1.5 AU from the Sun) is smaller than Earth and Venus
(0.107 Earth masses). It possesses an atmosphere of
mostly carbon dioxide with a surface pressure of 6.1
millibars (roughly 0.6% of that of Earth). Its surface,
peppered with vast volcanoes, such as Olympus Mons, and
rift valleys, such as Valles Marineris, shows geological
activity that may have persisted until as recently as 2 million
years ago. Its red colour comes from iron oxide (rust) in its
soil. Mars has two tiny natural satellites
(Deimosand Phobos) thought to be captured asteroids.
Outer Planets.
The four outer planets or giant planets (sometimes called
Jovian planets), collectively make up 99% of the mass known
to orbit the Sun. Jupiter and Saturn are each many tens of
times the mass of Earth and consist overwhelmingly of
hydrogen and helium; Uranus and Neptune are far less
massive (<20 Earth masses) and possess more ices in their
makeup. For these reasons, some astronomers suggest they
belong in their own category, "ice giants".All four giant
planets have rings, although only Saturn's ring system is
easily observed from Earth. The term superior
planet designates planets outside Earth's orbit and thus
includes both the outer planets and Mars.
Jupiter
Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of
all the other planets put together. It is composed largely
of hydrogen and helium. Jupiter's strong internal heat
creates semi-permanent features in its atmosphere, such as
cloud bands and the Great Red Spot. Jupiter has 67 known
satellites.
The
four
largest, Ganymede, Callisto, Io,
and Europa, show similarities to the terrestrial planets, such
as volcanism and internal heating. Ganymede, the largest
satellite in the Solar System, is larger than Mercury.
Saturn
Saturn (9.5 AU), distinguished by its extensive ring system,
has several similarities to Jupiter, such as its atmospheric
composition and magnetosphere. Although Saturn has 60%
of Jupiter's volume, it is less than a third as massive, at 95
Earth masses, making it the least dense planet in the Solar
System. The rings of Saturn are made up of small ice and
rock particles. Saturn has 62 confirmed satellites; two of
which, Titan and Enceladus,
show
signs
of
geological
activity, though they are largely made of ice. Titan, the
second-largest moon in the Solar System, is larger than
Mercury and the only satellite in the Solar System with a
substantial atmosphere.
Uranus
Uranus (19.2 AU), at 14 Earth masses, is the lightest of the
outer planets. Uniquely among the planets, it orbits the Sun
on its side; its axial tilt is over ninety degrees to the ecliptic.
It has a much colder core than the other giant planets and
radiates very little heat into space. Uranus has 27 known
satellites,
the
largest
being Titania,Oberon, Umbriel, Ariel, and Miranda.
Neptune
ones
Neptune (30.1 AU), though slightly smaller than Uranus, is
more massive (equivalent to 17 Earths) and hence
more dense. It radiates more internal heat, but not as much
as Jupiter or Saturn. Neptune has 14 known satellites. The
largest, Triton, is geologically active, with geysers of liquid
nitrogen. Triton is the only large satellite with aretrograde
orbit. Neptune is accompanied in its orbit by several minor
planets,
termed Neptune
1:1 resonance with it.
trojans,
that
are
in
Small Bodies in the Solar System
What Are Comets?
The sun, the planets, and their moons are not the only objects in
our solar system. There are also a large number of smaller bodies,
including comets, asteroids, and meteoroids. Scientists study
these objects to learn about the formation and composition of the
solar system. A comet is a small, loosely packed body of ice, rock,
and dust. The nucleus, or core, of a comet is made of rock, metal,
and ice. A comet’s nucleus can range from 1 km to 100 km in
diameter. A spherical cloud of gas and dust, called a coma,
surrounds the nucleus. The coma may extend as far as 1 million
kilometers from the nucleus.
COMET TAILS
A comet’s tail is its most spectacular feature. Sunlight changes
some of the comet’s ice to gas, which streams away from the
nucleus. Part of the tail is made of ions, or charged particles. The
ion tail, pushed by the solar wind, always points away from the
sun, no matter which way the comet is moving. A second tail, the
dust tail, follows the comet in its orbit. Some comet tails are more
than 80 million kilometers long, glowing brightly with reflected
sunlight.
COMET ORBITS AND ORIGINS
Remember that the planets move in elliptical, or oval shaped,
orbits. Comets also move in elliptical orbits. However, the orbits
of comets are much more stretched out than the orbits of planets.
Scientists think that many comets come from the Oort cloud. The
Oort cloud is a spherical cloud of dust and ice. It surrounds the
solar system, far beyond the orbit of Pluto. Pieces of the Oort
cloud may fall into orbits around our sun and become comets.
Some comets may also come from the Kuiper belt, a flat ring of
objects just beyond Neptune’s orbit.
COMPOSITION OF ASTEROIDS.
It is hard to determine what asteroids are made of. This is because
they are small and usually far away from Earth. Mostly, they are
composed of either rock or metal. Some asteroids may contain
carbon and carbon compounds. In general, asteroids do not have
a spherical shape because of their small size. Gravity must be
very strong to pull matter together into a spherical shape. Only
the largest asteroids are spherical.
What Are Meteoroids
Pieces of dust and debris from asteroids and comets, called
meteoroids, are scattered throughout the solar system. Most
meteoroids are about the size of a grain of sand. When a
meteoroid enters Earth’s atmosphere, it can reach a speed of up to
250,000 km/h. Friction with the atmosphere heats meteoroids and
the air around them, causing them to glow brightly. The glowing
trails that form when meteoroids burn up in the atmosphere are
called meteors. A meteor can be a few hundred meters in
diameter and tens of kilometers long before it fades. Sometimes, a
larger meteoroid enters the atmosphere. Some of these
meteoroids pass through the atmosphere without burning up
completely. When they reach Earth’s surface, they are called
meteorites.
TYPES OF METEORITES
Scientists classify meteorites based on composition. There are
three main types of meteorites: stony, metallic, and stony-iron.
Stony meteorites are similar to rocks on Earth. Some of them
contain carbon compounds similar to those found in living
organisms. Stony meteorites probably come from carbon-rich
asteroids. Metallic meteorites have a distinctive metallic
appearance and do not look like terrestrial rocks. They are made
mainly of iron and nickel. Stony-iron meteorites are made of a
combination of rocky material, iron, and nickel.
Three Major Types of Meteorites
1. Stony Meteorite: rocky material
2. Metallic Meteorite: iron and nickel
3. Stony-iron Meteorite: rocky material, iron, and nickel
Remember that asteroids and comets are probably made of debris
from the formation of our solar system. Meteorites are easier for
scientists to study than asteroids and comets. Because meteorites
are pieces of asteroids and comets, scientists study meteorites to
learn about the early solar system.
Galaxies
A galaxy is a gravitationally bound system of stars, stellar
remnants, interstellar gas and dust, and dark matter. The word
galaxy is derived from the Greek galaxias (γαλαξίας), literally
"milky", a reference to the Milky Way. Examples of galaxies range
from dwarfs with just a few thousand (103) stars to giants with
one hundred trillion (1014) stars, each orbiting their galaxy's
own center of mass. Galaxies can be categorized according to
their visual morphology, including elliptical, spiral,
and irregular. Many galaxies are believed to have black holes at
their active centers. The Milky Way's central black hole, known
as Sagittarius A*, has a mass four million times that of our Sun.
As of May 2015, EGS-zs8-1 is the most distant known galaxy,
estimated to be 13.1 billion light-years away and to have 15% of
the mass of the Milky Way.
There are approximately 170 billion (1.7 × 1011) galaxies in
the observable universe. Most of the galaxies are 1,000 to
100,000 parsecs in diameter and usually separated by distances on
the order of millions of parsecs (or mega parsecs).
The space between galaxies is filled with a tenuous gas with an
average density less than one atom per cubic meter. The majority
of galaxies are gravitationally organized into associations known
as galaxy groups, clusters, and super clusters. At the largest scale,
these associations are generally arranged into sheets and
filaments that are surrounded by immense voids.[
MILKY WAY GALAXY
The Greek philosopher Democritus (450–370 BC) proposed that
the bright band on the night sky known as the Milky Way might
consist of distant stars. Aristotle (384–322 BC), however, believed
the Milky Way to be caused by "the ignition of the fiery
exhalation of some stars that were large, numerous and close
together" and that the "ignition takes place in the upper part of
the atmosphere, in the region of the World that is continuous with
the heavenly motions. The NeoPlatonist philosopher Olympiodorus the Younger(c. 495–570 AD)
was critical of this view, arguing that if the Milky Way
is sublunary (situated between Earth and the Moon) it should
appear different at different times and places on Earth, and that it
should have parallax, which it does not. In his view, the Milky
Way is celestial.
According to Mohani Mohamed,
the Arabian astronomer Alhazen (965–1037) made the first
attempt at observing and measuring the Milky Way's parallax,
and he thus "determined that because the Milky Way had no
parallax, it must be remote from the Earth, not belonging to the
atmosphere. The Persian astronomer al-Bīrūnī (973–1048)
proposed the Milky Way galaxy to be "a collection of countless
fragments of the nature of nebulous stars.
The Andalusian astronomer Ibn Bajjah ("Avempace", d. 1138)
proposed that the Milky Way is made up of many stars that
almost touch one another and appear to be a continuous image
due to the effect of refraction from sublunary material, citing his
observation of the conjunction of Jupiter and Mars as evidence of
this occurring when two objects are near.
In the 14th century, the Syrian-born Ibn Qayyim proposed the
Milky Way galaxy to be "a myriad of tiny stars packed together in
the sphere of the fixed stars.
.
Actual proof of the Milky Way consisting of many stars came in
1610 when the Italian astronomer Galileo Galilei used
a telescope to study the Milky Way and discovered that it is
composed of a huge number of faint stars. In 1750 the English
astronomer Thomas Wright, in his An original theory or new
hypothesis of the Universe, speculated (correctly) that the galaxy
might be a rotating body of a huge number of stars held together
by gravitational forces, akin to the solar system but on a much
larger scale. The resulting disk of stars can be seen as a band on
the sky from our perspective inside the disk.. In a treatise in
1755, Immanuel Kant elaborated on Wright's idea about the
structure of the Milky Way.
The first project to describe the shape of the Milky Way and the
position of the Sun was undertaken by William Herschel in 1785
by counting the number of stars in different regions of the sky. He
produced a diagram of the shape of the galaxy with the solar
system close to the center. Using a refined approach, Kapteyn in
1920 arrived at the picture of a small (diameter about
15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A
different method by Harlow Shapley based on the cataloguing
of globular clusters led to a radically different picture: a flat disk
with diameter approximately 70 kilo parsecs and the Sun far from
the center. Both analyses failed to take into account the absorption
of light by interstellar dust present in the galactic plane, but
after Robert Julius Trumplerquantified this effect in 1930 by
studying open clusters, the present picture of our host galaxy, the
Milky Way, emerged.
Eclipse:
An eclipse is an astronomical event that occurs when
an astronomical object is temporarily obscured, either by passing
into the shadow of another body or by having another body pass
between it and the viewer. An eclipse is a type of syzygy.
The term eclipse is most often used to describe either a solar
eclipse, when the Moon's shadow crosses the Earth's surface, or a
lunar eclipse, when the Moon moves into the Earth's shadow.
However, it can also refer to such events beyond the Earth–Moon
system: for example, a planet moving into the shadow cast by one
of its moons, a moon passing into the shadow cast by its host
planet, or a moon passing into the shadow of another moon.
A binary star system can also produce eclipses if the plane of the
orbit of its constituent stars intersects the observer's position.
Solar eclipse
As observed from the Earth, a solar eclipse occurs when the Moon
passes in front of the Sun. The type of solar eclipse event depends
on the distance of the Moon from the Earth during the event. A
total solar eclipse occurs when the Earth intersects the umbra
portion of the Moon's shadow. When the umbra does not reach
the surface of the Earth, the Sun is only partially occulted,
resulting in an annular eclipse. Partial solar eclipses occur when
the viewer is inside the penumbra.
The eclipse magnitude is the fraction of the Sun's diameter that is
covered by the Moon. For a total eclipse, this value is always
greater than or equal to one. In both annular and total eclipses,
the eclipse magnitude is the ratio of the angular sizes of the Moon
to the Sun.
Solar eclipses are relatively brief events that can only be viewed
in totality along a relatively narrow track. Under the most
favorable circumstances, a total solar eclipse can last for
7 minutes, 31 seconds, and can be viewed along a track that is up
to 250 km wide. However, the region where a partial eclipse can
be observed is much larger. The Moon's umbra will advance
eastward at a rate of 1,700 km/h, until it no longer intersects the
Earth's surface.
Geometry of a total solar eclipse (not to scale)
During a solar eclipse, the Moon can sometimes perfectly cover
the Sun because its size is nearly the same as the Sun's when
viewed from the Earth. A total solar eclipse is in fact
an occultation while an annular solar eclipse is a transit.
When observed at points in space other than from the Earth's
surface, the Sun can be eclipsed by bodies other than the Moon.
Two examples include when the crew of Apollo 12 observed
the Earth to eclipse the Sun in 1969 and when
the Cassini probe observed Saturn to eclipse the Sun in 2006.
Lunar eclipse
The progression of a lunar eclipse from right to left. Totality is
shown with the first two images. These required a
longer exposure time to make the details visible.
Lunar eclipses occur when the Moon passes through the Earth's
shadow. This occurs only when the Moon is on the far side of the
Earth from the Sun, lunar eclipses only occur when there is a full
moon. Unlike a solar eclipse, an eclipse of the Moon can be
observed from nearly an entire hemisphere. For this reason it is
much more common to observe a lunar eclipse from a given
location. A lunar eclipse also lasts longer, taking several hours to
complete, with totality itself usually averaging anywhere from
about 30 minutes to over an hour.
There are three types of lunar eclipses: penumbral, when the
Moon crosses only the Earth's penumbra; partial, when the Moon
crosses partially into the Earth's umbra; and total, when the Moon
crosses entirely into the Earth's umbra. Total lunar eclipses pass
through all three phases. Even during a total lunar eclipse,
however, the Moon is not completely dark. Sunlight refracted
through the Earth's atmosphere enters the umbra and provides a
faint illumination. Much as in a sunset, the atmosphere tends to
more strongly scatter light with shorter wavelengths, so the
illumination of the Moon by refracted light has a red hue, thus the
phrase 'Blood Moon' is often found in descriptions of such lunar
events as far back as eclipses are recorded.
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